Treatment of aluminum alloys



Patented Dec. 20, 1932 UNITED STATES PATENT OFFICE noun 3. LANE, orNIAGARA rALLs, AND WILLIAM 'r. ENNOB, on MAssnNA, NEW

YORK, AssIoNons 'ro ALUMINUM coMrANY or AMnnIcA, orrrr'rsnunon, PENN-sYLvANIA, A conronA'rIoN or PENNSYLVANIA.

TREATMENT OF ALUMINUK ALLOYS No Drawing.

The invention relates to wrought products fabricated from aluminum basealloys and is particularly directed to a method of treating such alloysintermediate the working processes so as to produce a marked improvementin the final product.

The production and use of rivets made from aluminum base alloys hasincreasedfrom year to year coincident with the increase in production ofaircraft. In the field of surface transportation, on railroad vehiclesand motor busses, aluminum rivets are in increasing demand where theircorrosZon-resistance, lightness, and pleasing natural finish make themdesirable. A multitude of other uses might be mentioned.

In supplying this growing demand for aluminum rivets, the manufacturersthereof have encountered difliculties which, although innate and fairlcommon to the fabrfcation of aluminum shapes and articles by methodsinvolving the plastic deformation of metal, are accentuated by thesevere working operations by which aluminum rivets are fabricated. Thepresent invention is directed to the elim nation of these diflicultiesand, while it will hereinafterbe explained with reference to .thefabrication of aluminum rivets, it is applicable to the fabrication ofany aluminum shape or article where difiiculties of a nature like .orsimilar to those hereinafter described are encountered. r

In commercial processes of making aluminum rivets, the metal is usuallycast into ingots which are subsequently elon ated and reduced indiameter by known wor ing processes which form no part of this inventionand whose description is unnecessary to those versed in the art. Theproduct obtained by these working processes is, in its final stages, inthe shape of large diameter wire which is ultimately cut to "suitablelengths and passed through a rivet making machine wherein the head isformed on the shank, usually by a. single stamping operation, and thearticle is'ready for use. In this operation, there is a certain amountof wear sufiered -by the rivet forming dies and, although this is lookedupon as a necessary evil, means are continually sought for quantities ofrivets.

Application filed December 8, 1980. Serial No. 498,847.

reducing this wear and lessening the number of dies required in theproduction of set In addition to this, the rivet stock in the finalstages, and especially in the last head forming operation, is subject tocracking, slivering", bllsterin other defects well known to thosefamlliar with the operation, as well as the formation of an oxide filmconsequent to the heating and working processes, which oxide film tendsto augmentthe difficulties hereinabove enumerated. Sometimes the cracksare not visibleto the eye until the rivet head forming operationsubjects the metal to such a severe strain that the rivet head formedthereon is cracked and must be re'ected. In some. instances,'cracks inthe hea or shank of the rivet, quite capable of causing failure inservice, are discovered only after the most minute inspection.' It isapparent, therefore, that a distinct advantage would be-obtained by thepractically complete elimination of these disadvantages.

We have discovered a treatment which, applied in the stages intermediatethe final working processes, is effective in reducingto a substantialextent the number. of rivets cracked, sliveredor otherwise rendered deasa preferred method'an aqueous solution of sodium hydroxide of about 10per cent or 15 per cent concentration by weight at a temperature closeto the boiling point. Consid ering the wide variation in stock diameternecessitated by variation in dimensions of the final rivet, itis-impracticable to specify a set time of immersion but, usin as anindex the reduction in diameterof 't e wireby the action of thesolution, we have found substantial improvement with a reduction indiameter of only 0.005 inch while if more than usual trouble is beingencountered with the particular alloy and product as much 11.9001

inch may be removed. The desideratum is a smooth etched surface withoutpits and bright and free from oxide film, and simple experiment issufiicient in determining the beneficial reduction required. A

The coil of wire or other article should be rotatedor otherwise agitatedwhile in the caustic bath to insure even attack by the caustic. Afterseveral minutes, more or less, in the immersion bath, the stock iscleansed, by any convenient method, and we have found effective shoppractice to consist in a preliminary rinse in water, a momentary dip ina bath of nitric acid of a commercial concentration of about 37 percent, and a final wash in water after which the stock may be driedeither in air or low temperature drying oven. These latter washing anddrying details may, of course, be varied to suit commercial convenience,it being only desirable that traces of the caustic which would afl'ector attack the rivet forming dies be removed.

The caustic immersion is effective if applied either in the later wiredrawing stages or the ultimate pause immediately preceding the rivetforming operation. In any case, the improvement produced thereby isquite out of proportion to the few additional handling operationsnecessary, and we have found that by the use of 'our invention, rivetsmay be produced rapidly and efiiciently with considerably lessrejections 0r failures as a result of the forming operations, and withless wear on the dies.

The process has also been found applicable to certain difiicultfabrication operations both inethe final rolling of sheet and otherwrought products in the manufacture of which plastic deformation of themetal occurs. Unsightly blisters and surface defects of a more seriousnature are prevented in their inception by a caustic dip in intermediateforming processes substantially as above described. In all manner offorming and working operations which involve the plastic deformation ofmetal, advantages will accrue from use of the methods of our invention.

It is to be distinctly understood that wherever in this specification orin the claims appended hereto the term aluminum or aluminum alloy oraluminum base alloy 001 curs, it includes any alloy of aluminumcontaining morethan about 50 per cent aluminum. It is also to beunderstood that the term caustic solution, while herein usuallydescribed as consisting of a sodium hydroxide solution, is intended toinclude solutions of similar characteristics such as potassiumhydroxide, etc., the proper concentrations of which can easily bedetermined, this factor being significant to the extent thatit affectsthe time of immersion in the caustic bath.

1. A method of producing an improved wrought article formed from analuminum base alloy which comprises plastically deforming the metal ofsaid alloy by a series of metal working operations and immersing thepartially formed article in a caustic solution prior to the final metalworking operation. a

2. A method of fabricating an aluminum alloy rivet characterized bysubstantial freedom from surface defects incident to working, whichcomprises plastically deforming the metal of said aluminum alloy fromwhich said rivet is fabricated, said plastic deformation being effectedby a plurality of metal working operations, and immersing the partiallyformed rivet in a caustic solution prior to the final'metal workingoperation.

NORMAN B. LANE. WILLIAM T. EN N OR.

Having thus described our invention, we

claim

